Steels of the general composition described in U.S. Pat. Nos. 1,464,174, 2,331,900 and, most recently, 4,318,739 have been developed to a high degree of proficiency and today such steels have acquired a reputation in the closed die forging industry for quality and durability; indeed one, which is sold under the trademark FX, has long been recognized as a leading steel in this industry. In particular, the improvements in this steel attributable to U.S. Pat. No. 4,318,739 allowed the owner of said patent to warrant the steel against die failure, the only such warranty presently known in the industry.
Other applications of the above material include, but are not limited to, replacement machine parts such as gears, pinions, pistons and crankshafts. The up and running operating requirements for a steel for this application are somewhat similar to those of a die steel for closed die forging--high strength, high wear resistance, high hardenability and ease of machining. There are significant differences, however.
For example, some closed die forge shops neglect to preheat dies before the start of a production run. In cold weather, when a die is not used for an extended period of time, and is put into production without adequate preheating, catastrophic die failure can occur. To alleviate this mode of die failure typical closed die forging procedures require preheating the dies to a temperature above the brittle-to-ductile transition temperature before use, which may be approximately 300.degree. F. At typical closed die forging die temperatures the above-described steel has high impact toughness as well as high ductility.
One very important way in which machine part applications differ significantly from closed die forging die applications is that machine parts are used at room temperature, and therefore the ductility of the material at room temperature is much more critical than in die steel applications. Experience has shown, however, that the steel of U.S. Pat. No. 4,318,739, when used as a machine part, does not give the same superior performance as when used as closed forging die. In particular, it became apparent that improved room temperature ductility was highly desirable provided that the strength, wear resistance, hardenability, easy machinability and other beneficial characteristics of the steel, when used as a die steel, would not be sacrificed. By achieving increased room temperature ductility the steel could be truly termed to be a universal or dual steel in the sense that the steel maker could melt to one range and yet provide steel suitable for use in two substantially different applications, one requiring high room temperature ductility and the other not, while retaining all of the positive attributes of the die steel application--high strength, high wear resistance, high hardenability and ease of machining.